1. Field of the Invention
The present invention relates to torque wrenches, and particularly, to a torque wrench with constant torque, which maintains precise torque value during operation.
2. Description of the Related Art
Known structure of a torque wrench comprises a head for receiving a screw member, a hollowed shaft, a handle, and a clutching member disposed between the handle and the head. Through the adjustment of the handle against the hollowed shaft, the prestressed force of the clutching member upon the head is changed, whereby when the screw member received by the head bears a torque surpassing the prestressed force, the clutching effect is produced to limit the torque bore by the screw member, preventing the screw member from damaged.
However, said clutching member is disposed in the hollowed shaft in a manner of surface-contact, wherein the contacted dimension is relatively large. During the operation of the torque wrench, the prestressed force of the clutching member is dispersed on the contacted surface, whereby the prestressed force is not efficiently transmitted to the screw member received by the head; also, the torque feedback of the screw member is dispersed, causing the inaccuracy of the measured torque value, while the torque value is not maintained constantly. As a result, the screw member might be damaged after repeatedly used.